Discrepancy between totaliser and fuel gauges

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SPPMNC
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Discrepancy between totaliser and fuel gauges

Postby SPPMNC » Thu Jan 11, 2018 10:01 pm

Hello and a happy new year to everybody.
We are flying a brand new DA42-VI (came out of diamond factory in november 2017, less than 100h) and we got some problems with the fuel gauges.
In fact we fly 1h45 to 2h flights with full primary tanks (50 usg), on the ground the fuel gauges indicate 25 usg in each tank and the totalizer is reseted to 50 usg. When the totaliser indicates 39 usg the fuel gauges are already at 17 usg in each tank (34 usg total) and remain at this height until 26 usg on the totaliser when they suddenly drop to 13 and 13 usg. The totaliser seems to be always right considering how much fuel we put in the tanks when we refuel.
Has anyone had the same issue ? :scratch:
Greetings from New Caledonia
Malcolm
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dgger
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Re: Discrepancy between totaliser and fuel gauges

Postby dgger » Thu Jan 11, 2018 10:31 pm

I am pretty sure everyone of us is seeing the very same behaviour you describe. You have two fuel probes in each tank and the "in between the probes part" is where the fuel gauges tends to stick for a bit. The best way for me to deal with it is to be particularly careful to always reset the fuel counter when filling up. I rely on my fuel planning as well as the (extremely accurate) totalizer and only use the fuel gauges for sanity checks.
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SPPMNC
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Re: Discrepancy between totaliser and fuel gauges

Postby SPPMNC » Thu Jan 11, 2018 11:20 pm

Ok thank you for your answer. I sent a mail to Diamond Austria about it.
Do you know if Diamond already talked about this issue ?
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Re: Discrepancy between totaliser and fuel gauges

Postby ultraturtle » Thu Jan 11, 2018 11:30 pm

I concur with Peter. My -VI behaves the same (fuel quantity sticks between ~17-18 gal and 13 gal), but find the fuel gauges to be very accurate again once below 12 gallons.

I understand that the explanation for this behavior is that the fuel probes are only in the outboard and inboard tanks of each 3 tank assembly, not in the middle one.
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Re: Discrepancy between totaliser and fuel gauges

Postby dgger » Fri Jan 12, 2018 11:55 am

SPPMNC wrote:Ok thank you for your answer. I sent a mail to Diamond Austria about it.
Do you know if Diamond already talked about this issue ?

I am not sure, I understand, what you mean by "talked". This is expected behaviour resulting from a design decision. DAI is certainly aware of it.

Personally, I take no issue with it. I either visually check my tanks to make sure they are indeed topped off, or cross-check the totalizer as I am getting below 2 hours remaining. Works for me.
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Re: Discrepancy between totaliser and fuel gauges

Postby Colin » Fri Jan 12, 2018 6:50 pm

It's not just a design decision, it's a regulation decision made back when floats were the primary technology. So the regulation states that the fuel gauge must be accurate twice: when the tanks are full and when the tanks are empty. All the in between time it can be totally wrong (and, I would venture from my experience with a 1977 Warrior III, the gauges are rarely correct, half a tank is NOT what you have when the gauge is midway between full and empty).

A transducer is better technology, but still difficult to calibrate and there was no reason to add one to the "middle" tank.
Colin Summers, PP Multi-Engine IFR, ~2,300hrs
colin@mightycheese.com
http://www.flyingsummers.com
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N971RD DA40 G1000 s/n 40.508 (traded)
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Re: Discrepancy between totaliser and fuel gauges

Postby ememic99 » Sat Jan 13, 2018 1:50 am

This varies from the aircraft to the aircraft - some have less discrepancy. My gauges are pretty accurate below 16 gal in each tank, anything above that is just approximation. On top of that my totalizer is off by approximately 1 gal per hour, showing more fuel than I actually have on board.
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Re: Discrepancy between totaliser and fuel gauges

Postby Daneshgari » Sun Feb 25, 2018 2:08 am

Hi Everyone:

I have a brand new DA42 VI with only 60 hours on it. I picked it up in December 20th. Last week when I got topped off my left tank showed 5gl lower than the right tank. I tried everything and also, refueled again and the discrepancy still is there. I verified that the tanks where full by turning the auxiliary tanks on and it didn't go on indicating that the tanks are full. Anyone else has seen this?

Thanks
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Re: Discrepancy between totaliser and fuel gauges

Postby pietromarx » Sun Feb 25, 2018 2:35 am

Sounds like you need to do the fuel tank calibration procedure with the G1000. Do it when the tanks are nearly empty (so you don't have to drain them).
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Re: Discrepancy between totaliser and fuel gauges

Postby Daneshgari » Sun Feb 25, 2018 2:50 am

Thank you Peter. I wonder why this happened all of a sudden. Any thoughts?

Thanks Perry

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